Permanent magnet synchronous motor

ABSTRACT

A structure of a rotor used in a synchronous motor employing both of permanent magnets and a stator using concentrated windings is disclosed. Slits ( 13 ) provided in a section of a rotor laminated in a direction of a rotary shaft are shaped like an arc or a bow, and the shape protrudes toward an outside rim of rotor ( 12 ). Permanent magnets ( 14 ) are inserted into slits ( 13 ). This structure produces less magnetic salient poles than a conventional rotor, so that a magnetic flux density can be lowered, and an efficient motor with less loss is obtainable.

TECHNICAL FIELD

[0001] The present invention relates to a synchronous motor equippedwith both interior magnets and a stator using concentrated windings.

BACKGROUND ART

[0002]FIG. 11 shows a conventional synchronous motor equipped withinterior magnets and a stator using concentrated windings. In FIG. 11,the motor comprises stator 1 using concentrated windings, rotor 2, slits3 provided to the rotor, permanent magnets 4 buried in the slits. Stator1 is formed of a concentrated-winding stator having three phases, fourpoles and six slots. As shown in FIG. 12, respective teeth are woundwith windings independently, and each phase includes two coils 180degrees apart from each other, i.e., opposite to each other. Slits 3shaped like a flat plate are prepared inside rotor 2, and permanentmagnets having a similar shape to slit 3 are inserted in slits 3respectively. As shown in FIG. 12, a motor using the concentratedwindings provides independent windings to respective teeth, so that itscoil ends are smaller than those of a distributed-winding stator, wherethe windings straddle over plural teeth. Thus wire-wound resistancebecomes less, and copper loss caused by heat of the windings due tocurrent running through the motor can be reduced. As a result, a highlyefficient motor with smaller loss is obtainable.

[0003] The concentrated windings as shown in FIG. 11 have teeth woundwith coils respectively, and the coils of respective phases are adjacentto each other. This structure produces greater inductance. Combinationof this stator with a rotor having interior magnets produces magneticsalient poles in the rotor, so that reluctance torque becomes available.However, this structure increases inductance, and a lot of magnetic fluxflows into the flux path along axis “q”, and the flux path pulls themagnetic flux into the rotor as shown in FIG. 11. Thus a magnetic fluxdensity of the core substantially increases. As a result, iron lossgreatly increases although the copper loss decreases, so that efficiencyis lowered, which turns the advantage of the concentrated windingsinsignificant. The present invention addresses the foregoing problem,and aims to provide a rotor of a synchronous motor having theconcentrated windings. This rotor advantageously lowers the magneticflux density of the stator core, and yet reduces copper loss and ironloss.

DISCLOSURE OF INVENTION

[0004] The present invention provides a rotor of a synchronous motorhaving both of permanent magnets and a stator using a concentratedwinding method. On a section of the rotor laminated in a rotary shaftdirection, arc-shaped or bow-shaped slits are provided. The projectingportion of the arc-shape or bow shape face to the outside rim of therotor, and permanent magnets are inserted into the slits. This structureproduces less magnetic salient poles than a conventional rotor, therebyreducing a magnetic flux density of the stator core. This structure canthus provide a highly efficient motor that incurs less loss.

[0005] V-shaped slits instead of the arc- or bow-shaped slits canproduce a similar advantage. In this case, a vertex of acute angle ofthe V-shape faces to the outside rim of the rotor. Further, two sheetsof permanent magnets can be inserted into each one of the V-shapedslits, so that a cost of the magnets is reduced. As a result, anefficient and inexpensive motor is obtainable.

[0006] Magnets used in the present invention can be any magnets such asferrite magnet, rare-earth magnet or the like regardless of magnetmaterials; however, a structure employing the rare-earth magnet, whichproduces strong magnetic force among others, can reduce iron loss, sothat the greatest advantage can be expected. Dividing the rare-earthmagnet axially into plural magnets reduces loss due to eddy-currentrunning on magnet surface, so that further efficient motor isachievable.

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0007]FIG. 1 shows a sectional view of a motor in accordance with afirst exemplary embodiment.

[0008]FIG. 2 is a partially enlarged view of a rotor of the motor inaccordance with the first embodiment.

[0009]FIG. 3 is an enlarged view of teeth of the motor in accordancewith the first embodiment.

[0010]FIG. 4 illustrates magnetic flux densities of the motor inaccordance with the first embodiment.

[0011]FIG. 5 illustrates magnetic flux densities of a conventionalmotor.

[0012]FIG. 6 compares iron loss produced in the first embodiment withthat produced by a conventional motor.

[0013]FIG. 7 shows divided permanent magnets.

[0014]FIG. 8 shows a conventional motor.

[0015]FIG. 9 shows a sectional view of a motor in accordance with asecond exemplary embodiment.

[0016]FIG. 10 shows a compressor in accordance with a third exemplaryembodiment.

[0017]FIG. 11 shows a sectional view of a conventional motor.

[0018]FIG. 12 illustrates conventional concentrated windings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Exemplary embodiments of the present invention are demonstratedhereinafter with reference to the accompanying drawings. The embodimentsbelow are exemplary reductions to practice of the present invention, andnot to limit the technical scope of the present invention.

[0020] Exemplary Embodiment 1

[0021]FIG. 1 illustrates the first exemplary embodiment, where stator 11employing concentrated windings, rotor 12, slits 13, and permanentmagnets 14 buried in the slits are used. Stator 11 has three phases,four poles and six slots. Each one of teeth is wound independently witha winding, and two coils of each phase are apart 180 degrees from eachother, i.e., opposite to each other. Stator 11 is formed by laminatingplural electromagnetic steel sheets in a rotary shaft direction, andincludes plural teeth. Ends of each one of teeth 15 slightly encroachinto slots as shown in FIG. 3.

[0022] To be more specific, distance “r” between arc face 16, whichfaces to rotor 12, of stator 11 and the center of rotor 12 is smaller ata center portion of teeth 15 than at the end of teeth 15. (The brokenline tangent to arc face 16 measures a constant distance “r” from thecenter of rotor 12.) This structure restrains demagnetizing field fromflowing to rotor 12. Because adjacent teeth of the concentrated windingsbecome different poles from each other, and inductance increases, sothat demagnetizing field tends to be applied to rotor 12. In order toovercome this phenomenon, both the ends of each one of the teethslightly encroach into slots for enlarging air-gap at the ends of theteeth.

[0023] Each one of slits 13 prepared inside rotor 12 is shaped like anarc and protruded toward outside rim of rotor 12. A distance betweenslit 13 and outside rim of rotor 12 is narrower at the center of slit 13and becomes gradually wider toward both the ends of the slit. At theouter most end, the distance becomes narrow again.

[0024] Permanent magnets 14 are buried in slits 13, and the most outerboth ends of each one of slits 13 remain void as non-magnetic portions,which work as leakage flux preventing sections that can prevent leakageflux from occurring between the adjacent permanent magnets. Thenon-magnetic portions are not necessarily the voids, but resin can beburied there.

[0025] As shown in FIG. 2, permanent magnet 14 protrudes its centerportion A toward the outside rim of rotor 13 from the line runningthrough both ends B of the magnet. This shape of permanent magnet 14prepares narrower space “a” between magnet 14 and rotor 12 at its centerthan space “b” at both its ends. This structure substantially narrowsthe flux-path width along axis “q” of the first embodiment than that ofthe conventional rotor. The inductance of axis “q” thus decreases, sothat an amount of magnetic flux along axis “q” running inside the rotoris reduced. As a result, the magnetic flux density of the stator corewhen it is loaded can be lowered. FIG. 4 and FIG. 5 compare the magneticflux density of the rotor of the present invention when it is loadedwith the magnetic flux density of a conventional rotor. The rotor of thepresent invention has lower magnetic flux densities at its teeth andyoke of the stator core than those of the conventional rotor. Since theiron loss increases as the frequency and the magnetic flux densityincrease, the motor of the present invention obtains a great advantageparticularly when the motor is loaded or spun at a high speed.

[0026]FIG. 6 compares iron loss produced in the first embodiment withthat produced by a conventional motor. This graph shows the number ofrotations of the motor on the X-axis and the iron loss produced by themotor on the Y-axis. As shown in FIG. 6, the rotor of the presentinvention produces less iron loss than the conventional one, thus ahighly efficient motor producing a little loss can be provided. Thegraph shows that the iron loss decreases in a greater amount as thenumber of rotations increases, in particular, the loss decreasesadvantageously at a high speed rotations faster than 3000 r/min.

[0027] In the first embodiment, one piece of permanent magnet is buriedin each one of the slits. However, the stator having concentratedwindings tends to produce eddy current, so that as shown in FIG. 7 thepermanent magnet is divided into plural pieces in the direction of therotary shaft before they are buried. Thus the path length of eddycurrent running on magnet surface can be shortened, whereby loss due tothe eddy current is substantially reduced. The rare-earth magnetadvantageously reduces the eddy-current loss.

[0028] Japanese Patent Application Non-Examined Publication No.H05-304737 discloses a motor with permanent magnets shown in FIG. 8,apparently similar to the motor in accordance with this embodiment;however, the disclosed motor uses a stator with distributed windings.Since the stator used in this first embodiment employs the concentratedwindings, adjacent poles have different polarities. The inductance thusbecomes greater, which invited the present invention. However, thestator employing distributed windings does not have such a problem, thusthe foregoing publication cannot anticipate the present invention.

[0029] Exemplary Embodiment 2

[0030]FIG. 9 illustrates the second embodiment of the present invention.In FIG. 9, stator 21 employs a concentrated winding method, V-shapedslits 23 are formed in rotor 22, permanent magnets 24 are buried in theslits. The vertex of each one of the V-shaped magnets faces toward theoutside rim of the rotor. This structure also can narrow the flux pathalong axis “q” as discussed in the first embodiment, and thus can lowerthe iron loss. This structure produces a similar advantage to the firstembodiment. Further, as shown in FIG. 9, the permanent magnet to beburied in each slit is divided in half, and two sheets of magnet shapedlike a flat plate can be inserted into the slit. Thus an efficient motorof a lower cost, which uses inexpensive and flat magnets instead ofexpensive and arc-shaped magnets shown in FIG. 1, can be obtained.

[0031] The V-shaped magnet shown in FIG. 9 uses two sheets of permanentmagnet in one slit, so that a void is formed between the magnets formingthe V-shape. The two sheets of magnet form one magnetic pole.

[0032] Exemplary Embodiment 3

[0033]FIG. 10 shows sectional view of a compressor which employs thesynchronous motor having permanent magnets in accordance with the firstexemplary embodiment. As shown in FIG. 10, the compressor comprisesstator 11 using the concentrated windings, rotor 12, permanent magnets14, accumulator 31 and compressing mechanism 32. The motor of thiscompressor has a shorter length including its coil end, and worksefficiently, so that the compressor is best fit for a place where thepower or the storage area is limited, such as an air-conditionercompressor used in an electric vehicle.

[0034] Industrial Applicability

[0035] In a motor having interior magnets and a stator employing theconcentrated windings, a distance between the outside rim of the rotorand a slit, in which a permanent magnet is buried, is narrower at acenter portion of the slit than at both the ends of the slit. Thisstructure reduces a magnetic flux density of the stator core, so that amore efficient motor with less iron loss than conventional motors isobtainable.

1. (Re-amended) A synchronous motor employing permanent magnetscomprising: a stator having teeth on which conductive windings are woundin a concentrated manner; and a rotor having permanent magnets buried inslits to form magnetic poles, wherein a flux path formed of magneticmaterial is provided between each one of the magnetic poles and outsiderim of said rotor, a center portion of each one of the magnetic polesprotrudes outer toward the outside rim of said rotor than ends of eachone of the magnetic poles, a space of the flux path between the outsiderim of said rotor and each one of the magnetic poles is narrower at thecenter portion than at the ends of the magnetic poles thereby regulatingan amount of magnetic flux flowing into the flux path.
 2. (Deleted) 3.The synchronous motor employing permanent magnets as defined in claim 1,wherein a slit in which each one of the permanent magnets is buried isshaped like a letter “V” protruding toward the outside rim of saidrotor.
 4. The synchronous motor employing permanent magnets as definedin claim 3, wherein a plurality of the permanent magnets shaped likeflat plates are arranged in the letter “V” to form the magnetic poles.5. The synchronous motor employing permanent magnets as defined in claim1, wherein a slit in which each one of the permanent magnets is buriedis shaped like a bow protruding toward the outside rim of said rotor. 6.(Already deleted at the first amendment).
 7. (Amended) The synchronousmotor employing permanent magnets as defined in claim 1, wherein eachone of the permanent magnets buried in a slit is divided into aplurality of sheets in a direction of a rotor shaft.
 8. The synchronousmotor employing permanent magnets as defined in claim 1, wherein themotor spins at a rotating speed not less than 3000 rpm.
 9. Thesynchronous motor employing permanent magnets as defined in claim 1,wherein a distance between a center of said rotor and a face of each oneof the teeth opposite to said rotor is wider at an end of the teeth thanat a center portion of the teeth.
 10. The synchronous motor employingpermanent magnets as defined in claim 1, wherein the motor spins usingreluctance torque.
 11. (Amended) The synchronous motor employingpermanent magnets as defined in claim 1, wherein the teeth include afirst coil formed by winding a conductive winding in the concentratedmanner on a first tooth and a second coil formed by winding a conductivewinding in the concentrated manner on a second tooth adjacent to thefirst tooth, and the first and the second coils powering the conductivewindings have different polarities from each other.
 12. A compressordriven by the motor as defined in claim
 1. 13. A freezing cycleemploying the compressor as defined in claim
 12. 14. A car employing acar air-conditioner driven by the compressor as defined in claim 12.